1. Field of the Invention
The present invention relates to an electrostatic actuator used as a drive mechanism of an inkjet head or the like, a droplet ejection head having the electrostatic actuator, and a droplet ejection device having the droplet ejection head.
2. Related Art
Generally, a droplet ejection head with an electrostatic actuator has a pressure-generating chamber for ejecting droplets by applying pressure. By giving an elastic displacement to part of the pressure-generating chamber (a diaphragm) using an electrostatic force, a pressure for ejecting droplets from an opening of a nozzle is generated.
In recent years, inkjet heads (which are a typical example of the above type of droplet ejection head) have been employing an increasing number of nozzles to accommodate fast-speed printing. In addition, in response to a demand for higher resolutions, drive mechanisms (actuators) of very small sizes have been required. As described above, as the drive mechanism becomes smaller and denser, the area of the diaphragm of each pressure-generating chamber becomes smaller, and therefore the developed pressure in the pressure-generating chamber caused by the displacement of the diaphragm also becomes smaller, which further reduces the energy given to droplets to be ejected. In this case, securing stability in droplet-landing becomes difficult because the mass of dispensed ink is reduced, accompanied by the reduction of the dispensing speed. Therefore, it has been requested to increase the developed pressure in the pressure chamber by increasing the amount of displacement of the diaphragm.
Further, as an inkjet recording head aiming to secure the traveling speed of ink droplets and to control the displacement of the diaphragm, there is a technique, regarding a substrate placed opposite the substrate having the diaphragm, to make a two-tiered concavity, which is provided to configure a vibration chamber for the diaphragm, by scraping in two levels forming a shallow concavity and a deep concavity, wherein an electrode is provided for each concavity (refer to Japanese Unexamined Patent Publication No. 10-286952, for example).
According to the above technique, due to the configuration having a deep concavity as well as a shallow concavity, a larger displacement of the diaphragm can be secured compared to a technique which employs only a shallow concavity. Therefore, such a configuration is expected to contribute to the improvement of developed pressure inside the pressure chamber.
However, like the technique in Japanese Unexamined Patent Publication No. 10-286952, forming a plurality of concavities with different depths on an oppositely placed substrate requires a plurality of photoresist pattern alignment processes. In such photoresist pattern alignment, a small amount of error occurs in the actual process. Therefore, a configuration having a plurality of concavities requires a dimensional component design where a potential error occurring in each concavity formation step is taken into consideration, which leads to a result contradicting the concept of smaller size and higher density drive mechanisms.
The present invention has been developed in consideration of such a problem and is intended to provide a simply-manufacturable electrostatic actuator that can increase the displacement amount of the diaphragm and can therefore improve ejection pressure when used as a drive mechanism of a droplet ejection head. In addition, the present invention aims to provide a droplet ejection head and a droplet ejection device having such an electrostatic actuator.